Solar power systems, such as concentrated photovoltaic cell-based solar power systems and solar-thermal systems, provide an optimum power output when they are precisely aligned with the sun. Flat panel photovoltaic systems lacking concentrators also benefit from sun alignment. Therefore, solar power systems may be mounted on solar tracking systems that are configured to maintain alignment between the associated solar power systems and the sun as the sun moves across the sky.
A concentrated photovoltaic (“CPV”) cell typically includes a photovoltaic element that produces electric power from incident sunlight, and a focusing element that concentrates the sunlight falling over a protracted area onto the cell. The focusing element should be pointed accurately toward the sun, within better than a degree, and should move with the sun in a sun tracking manner. CPV cells are generally grouped in arrays such that the CPV cells are pointed toward the sun when the array is pointed toward the sun.
A typical solar tracking system includes electric motors, gears, sensors, processors and angular position encoders, all of which substantially increase the initial capital cost and present reliability and on-going maintenance issues, thereby increasing the cost of generated electricity. For example, a conventional solar tracking system uses sun sensors, such as photodiodes, pixel cameras or the like, that are mounted in view of the sun and are exposed to the environment. Such sun sensors are arranged to indicate the sun position relative to the array. However, such sun sensors generally have pointing vectors that are skewed from that of the array, thereby requiring calibration in two-dimensions—a non-trivial operation. Once calibrated, the array is moved to track the sun by motors in a closed loop manner with the sun sensor outputs. Therefore, the use of sun sensors introduces the need for on-going maintenance, such as cleaning the optical elements of the sun sensor and maintaining the sun sensor aligned with its original pointing vector.
Another conventional approach to solar tracking uses the calculable sun position as a function of array latitude/longitude and time. Once the sun zenith and azimuth position is known, angle encoders having sub-degree resolution provide array orientation feedback to point the array toward the sun. However, angle encoders are expensive and must be protected from the environment. Furthermore, a calibration step is required to determine the array pointing vector with respect to the angle encoder outputs.
Ideally the electronics of a solar tracking system are mounted within a single environment protecting enclosure with a minimum of external sensors (such as limit switches, sun sensors and angle encoders) and cables and requisite connectors. Motors for changing the array orientation are unavoidably remote.
Accordingly, those skilled in the art continue to seek new solar tracking systems, including solar tracking systems that provide precise solar alignment without the expense, maintenance and reliability issues associated with sun sensors, angle encoders, limit switches, and such.